I looked at Merriam dictionary but there are no notes on usage and the three words are synonyms. I want to talk about encouraging the development of certain qualities in people, like honesty or bravery. Does it make any difference whatsoever which word I use?
p.s. I have seen some people even use the word nourish but google search shows me that usage is less frequent and perhaps more useful for feeding actual things (like plants) not qualities.
Best Answer
The three terms really do convey essentially the same meaning. "Nurture" is somewhat more intimate, perhaps best suited to someone close to you (or yourself):
To talk about "cultivating" people is mildly insulting, as people are not crops, but it would be appropriate to say something like
"Foster," or to promote, is neutral and would also be appropriate for a business or teaching environment:
Another associated word that you might find useful is "instill," or to introduce or implant:
As you note, "nourish" may not be as well suited because qualities such as honesty are not in themselves nourishing (although your attention and encouragement could very well be emotionally nourishing).